A 72 year-old female patient is presented in whom delusional depression, a possible distinct subtype of depressive illness characterized by a selective decrease of cerebrospinal fluid (CSF) norepinephrine (NE) metabolism, preceded the onset of Parkinsonism by several years. The report suggests that delusional depression may be a particular manifestation of depressive illness in Parkinsonian patients. In addition, since the activity of plasma and cerebrospinal fluid (CSF) dopamine beta-hydroxylase (DBH) is genetically determined, the co-occurrence of delusional depression and Parkinsonism in this patient may be related to a common underlying genetic defect that expresses itself biochemically by reduced cerebral NE metabolism.